A known clutch mechanism is shown in FIG. 1. This forms a unitary assembly and comprises at least one pressure plate 17, a cover 13 and a resilient diaphragm 20 having an axial action disposed between the cover and the pressure plate.
The cover 13 is adapted to be fastened to the reaction plate 11 of a clutch fixed to the driving shaft of the vehicle, whilst the pressure plate 17 is axially movable relative to the cover and is fixed in rotation with the latter.
The diaphragm 20 bears on the cover 13 and on the pressure plate 17 to urge the said plate towards the reaction plate 11 and to clamp, between the said plates 11 and 17, friction linings of a torsion damper 12 connected in rotation with the input shaft of the gearbox.
The diaphragm 20 comprises a peripheral part forming a "Belleville" washer 21, and a central part divided into radial fingers 24 by slots which open out into wider holes 50 disposed on the internal periphery of the "Belleville" washer part of the diaphragm.
In operation, especially when the clutch is engaged, heat is produced as a result of the friction between the plates 11, 17 and the linings of the torsion damper 12.
This heat may result in instability in the transmission of torque and is detrimental to the life of the friction linings.
In order to overcome this disadvantage, a device comprising a plurality of cooling flanges disposed at the internal periphery of the cover has been proposed in FR-A-2 560 950 (U.S. Pat. No. 4,657,128), the said flanges being inclined towards the interior of the cover.
This arrangement is not completely satisfactory, since the flanges are disposed facing the fingers of the diaphragm.